1. Field of the Invention
This invention relates generally to oil and gas well tubing and more particularly has to do with the construction of high pressure tubular joints operable when made-up and run into a well to withstand extreme fluid pressures, both internal and external, that seek escape through the tubular assembly at the joints.
2. Description of the Prior Art
The search for oil and gas reserves has brought about the exploration of ever deeper formations. These deeper formations require longer strings of the production pipe, casing, liners and drill pipe used in the exploration and production of oil and gas at extremely high pressures. This increased length of tubular strings imposes the upper portion of the string to very high tensile loads and in addition, the tubular strings are exposed to extremes of pressure both from within the tubing and also from the exterior of the tubing.
Prior art metal-to-metal sealing mechanisms have provided seals that resist mainly internal pressure or mainly external pressure, as long as the surrounding tubular geometry remains in the elastic range. The prior art sealing mechanisms have not solved the sealing problem of withstanding extremes of internal pressure, or external pressure, either pressure acting during circumstances of high tension, torque or compression forces acting on the tubing.
U.S. Pat. No. 2,992,019 to M. D. MacArthur shows a casing joint having metal-to-metal sealing means responsive primarily to extremes of inside fluid pressure. The disclosed interior sealing for the pin and box provides a fourteen degree (14.degree.) interior seal that is spaced a distance from the threaded inner connection to enable the deformation or strain on the pin, in response to the inside fluid pressure, to flex the pin interior sealing surface against the box interior sealing surface and obtain a greater sealing force. In addition, during such strain, the sealing contact area decreases which increases the sealing force over the reduced area. In particular, the distance between the pin and the seal surface remains the same while the center of the sealing area moves slightly toward the thread during such sealing flexing.
U.S. Pat. No. 4,009,893 issued to Schatton, et al. discloses a tubing or casing joint with box and pin members having two axially spaced thread sections separated by a radial step zone which includes for the pin member, an annulus having an axial undercut. The endface of the annulus bears against a complementary face in the step zone of the box member and serves to act as a complementary thread stopface, in addition to a stopface at the end of the pin member and in the box member.
There has been a long-felt need for metal-to-metal sealing mechanisms for use in tubular joints which are able to hold mating members together for complete leak resistance against both internal and external pressures, regardless of the force of tension, compression, internal pressure, external pressure, torque or any combination thereof that are applied to the joint.
It is therefore a primary object of this invention to provide a trapping mechanism in a joint to hold the mating members together for complete leak resistance in the face of multiple forces acting on the joint.
Not only must the joint be sealed, it must be capable of being made up and disassembled numerous times without galling and without the danger of stripping threads or cross-threading. It is of course, desirable and therefore an advantage of the joint according to the invention disclosed herein in that it may be "stabbed" and that thereafter it can be made up with a relatively small number of turns.
It is common to use an integral or upset joint wherein the threaded portion of the pipe is thickened by a forging technique so as to provide more metal in the area where threads are cut. The invention disclosed below may advantageously be used with an integral or upset type of joint, and it may also be used with a threaded and coupled joint wherein both ends of the tubular elements are provided with male joining elements and a coupling member is provided with female joining elements.